edit background layer in png

I have an image here a guy http://andybriggs.com/img/streetguy.png. I'm not good at image editing so I don't know if I'm explaining this right. The image is a rectangle and is one layer when开发者_如何学JAVA opened in gimp. I want to change the white background to gray so it will match the background color on my website. Does that make sense?

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Never mind I figured it out on GIMP:

From the toolbar: Layer >> New from Visible; This gives you the foreground layer (the guy) and another layer with the white background.

Then click the second layer, the background, and go to the paint bucket and click it on the image.

Then go to the Layers, Channels window and in the layers pane click the eye image on the first layer to make it invisible. Then go to Image >> Flatten Image and it's done